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            <h1 style="text-align: center;"><big><big><big><a
 name="file_do_not_compress_solutions"></a>Why I cannot compress some
types of files (avi, mp3, pdf...)<br>
            </big></big></big></h1>
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                  <ul>
                    <li>
                      <p><a href="#cannot_compress_files">WHY
SOME FILES CANNOT BE EFFICIENTLY COMPRESSED?</a></p>
                    </li>
                  </ul>
                  </td>
                  <td style="vertical-align: top; width: 128px;">
                  <h2><img alt="can not compress files"
 title="How to reduce size of files with poor compression ratio, solutions for  AVI, DOCX, JPEG, MP3, MPEG, PDF..."
 src="file-format/tips-tricks.png" style="width: 96px; height: 96px;"
 align="right"></h2>
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            <div style="text-align: left; color: rgb(0, 0, 0);">
            <h2><big><big><big><a name="cannot_compress_files"></a><a
 href="#file_do_not_compress_solutions">Why
some files cannot be efficiently compressed?</a></big></big><br>
            </big></h2>
            </div>
            <br>
It is a quite common experience that not all file types can be
compressed with equal efficiency: some data structures, like text
files, or text based containers (spreadsheets, documents, databases)
usually compresses well, reaching high compression ratio, while other
formats, usually multimedia files,
does not compress properly and reaches very poor compression ratio not
matter how powerful (and slow)
compression method is used.<br>
Most common reasons why a file can't be efficiently compressed are:<br>
            <table style="width: 100%; text-align: left;" border="0"
 cellpadding="24" cellspacing="0">
              <tbody>
                <tr>
                  <td style="vertical-align: middle;">
                  <h2><span style="font-weight: bold;"><img
 title="Non optimal file content leads to poor data compression level"
 alt="cannot reduce size of file with compression"
 src="file-format/one.png" style="width: 48px; height: 48px;"></span></h2>
                  </td>
                  <td style="vertical-align: middle;"><span
 style="font-weight: bold;">The file contains lots of non significant
or duplicate data, or noise</span><br>
Some data in the file may be not relevant and should be edited off
(with the own editing tools appropriate for the input file type) before
archiving the data, in order to reduce disk occupation without losing
actual information.<br>
                  <br>
                  <span style="font-weight: bold;">Some miscellaneous
examples of non-meaningful data in files</span><br>
                  <ol>
                    <li><a name="can_not_compress_disk_images"></a><a
 href="optimize-virtual-machines-backup-images.html">Disk images /
virtual machine disks</a>
(QCOW2, VMDK, Microsoft VHD, VDI) often contain data which should be
cleared, as recycle bin files, temporary files, RAM content (if machine
was stopped rather than being shut down), and data of erased files
still written on disk sectors if free space is not overwritten by zero
- not shown in disk occupation when running the image, as marked as
free space after deletion.</li>
                    <li><a name="can_not_compress_database"></a>Databases
can contain deleted entries until
purged with
appropriate actions for specific database format; also, running proper
data duplication routines is a good
practice before archiving / backing up the database.</li>
                    <li><a name="can_not_compress_backup_file"></a>Backup
should be checked to reduce occurrencies
of duplicate or
temporary files, incremental backup strategy (save only files modified
between the two backup checkpoints) can be employed to dramatically
reduce the size of backup sets.<br>
                    </li>
                    <li><a name="can_not_compress_docx_pdf_files"></a>Document
files (MS Office DOCX, Adobe Acrobat
PDF...) can contain data of obsolete
revisions, or
multimedia data not matching the resolution of the document which
should be authored to a more appropriate definition / size either on
source multimedia files, or during document editing.<br>
                    </li>
                    <li><a name="can_not_compress_multimedia_files"></a>Graphic
and multimedia can contain high level
of enthropy <a target="_blank"
 href="http://en.wikipedia.org/wiki/Entropy_%28information_theory%29">entropy<img
 alt="information theory compression" title="Data entropy Wikipedia"
 src="free-rar/extractor.png"
 style="border: 0px solid ; width: 12px; height: 10px;"></a>
that should be accurately taken in account, in example a poor quality
photo sensor or a not adequate microphone may lead to low signal /
noise ratio, which will lead boot to a poor result and poorly
compressible data.<br>
                    </li>
                  </ol>
                  <h3><span style="font-weight: bold;">How to reduce
size of data before compression</span></h3>
It is recommended to use specific editing tools for the format or the
scope, before starting actual compression.<br>
PeaZip free archiver can help in some of those tasks providing tools to
                  <a href="secure-delete.html">zero free space</a>, <a
 href="duplicates-hash-checksum.html">find and remove duplicate files</a>,
and to <a href="compress-resize-jpeg-png-files.html">resize, convert
and re-compress graphic files</a>.</td>
                </tr>
                <tr>
                  <td
 style="text-align: center; vertical-align: middle;">
                  <h2><span style="font-weight: bold;"><img
 title="Unable to compress already compressed files, archives, and multimedia data"
 alt="cannot compress multimedia files" src="file-format/two.png"
 style="width: 48px; height: 48px;"></span></h2>
                  </td>
                  <td style="vertical-align: middle;"> <span
 style="font-weight: bold;">The file is
already compressed</span><br>
Some file formats are designed with built in compression, so no further
compression is possible (or practical).<br>
File size is already efficiently reduced by design often employing
dedicated compression types (<a
 href="lossless-compression-lossy-compression.html">lossy compression</a>
is common in compressed multimedia files), more efficient than general
purpose compression algorithms designed to work on a plurality of data
structures.<br>
                  <br>
                  <h3><span style="font-weight: bold;">Examples of
already
compressed file formats</span></h3>
Graphic files as JPEG and PNG, will usually compress poorly compared to
uncompressed bitmap graphic as RAW, BMP and uncompressed TIFF files
(read more on <a href="compress-resize-jpeg-png-files.html">how to
optimize compression of images</a>).<br>
                  <a name="can_not_compress_mp3_files"></a>Audio files
as MP3, will usually compress very poorly compared to
uncopmpressed audio formats like WAV files, and multimedia video files
like AVI,
DIVX, MPEG, MKV...&nbsp; are very poorly compressible.<br>
                  <a name="can_not_compress_pdf_files"></a>Some
document types as Adobe Acrorbat PDF, Open Office formats, and new
Microsoft
Office file formats (DOCX, XLSX, PPTX...), and some databases, contains
already compressed data (usually employing lossless
compression designed around Deflate algorithm), and generally does not
compress
well compared to older uncompressed documents formats, like DOC, XLS,
PPT...<br>
                  <a name="reduce_size_of_docx_pdf_xlsx_files"></a>Please
note a document or database is itself a container, so if it
stores compressed bitmap graphic and other multimedia data,
as a role of thumb it will compress poorly if compared to file
of same format containing plain text data, this is the reason why even
some uncompressed documents (DOC, XLS,
PPT) will compress less than other documents of the same type.<br>
                  <br>
                  <h3><span style="font-weight: bold;">Possible
solutions
to compress already compressed files</span></h3>
                  <ol>
                    <li><a name="can_not_compress_zip_file"></a>Extract
existing archives (ZIP, ACE, ...) and
recompress the content in a more powerful compression format, such as
RAR or 7Z: in this case the final archives will be smaller than the
original ones (depending on the nature of the input data), while trying
to compress the archives will not provide comparable results. PeaZip
can automate extraction and re-compression of existing archives using
stronger compression, using its <a href="convert-files.html">file
conversion tool</a>. </li>
                    <li>In some cases the built-in file format
compression is a trade off between the need to reduce the final size of
the file and the need to quickly access the content of the file,
avoiding excessively powerful and complicate compression algorithms. In
those cases
(i.e. JPEG, PDF, DOCX, XLSX files...) applying a powerful compression
(i.e.compress to RAR or 7Z) can reduce the size of those files.<br>
                    </li>
                    <li>In worst cases it is simply not possible to
further improve current compression level of the files, and other
strategies should be considered, i.e. use utilities like PeaZip to
deduplicate files (search for
identical files to avoid archiving / backing up multiple copies of the
same data), or <a href="file-split.html">split output archive in
multiple volumes</a> of desired size if it is needed to keep the output
under mandatory maximum sizes (i.e. <a target="_blank"
 href="http://en.wikipedia.org/wiki/Email_attachment#Size_limits">maximum
e-mail
attachment size<img alt="maximum email size allowed"
 title="Attachment size limit" src="free-rar/extractor.png"
 style="border: 0px solid ; width: 12px; height: 10px;"></a>, max
upload
files size, filesystem limits or built-in <a
 href="rar-zip-file-format-size-limitations.html">file size limitations</a>,
etc). Also in those cases it may be
useful to opt for a lower compression settings (or no-compression
archiving, option generally labelled as "store" compression level),
which will save time and computing power with no practical inpact on
final file size.</li>
                  </ol>
                  </td>
                </tr>
                <tr>
                  <td style="vertical-align: middle;">
                  <h2><span style="font-weight: bold;"><img
 title="Solutions to save space while working with non compressible data"
 alt="why some files types does not compress efficiently"
 src="file-format/three.png" style="width: 48px; height: 48px;"></span></h2>
                  </td>
                  <td style="vertical-align: top;"> <span
 style="font-weight: bold;">The file is not
compressible at all</span><span
 style="background-color: rgb(255, 238, 221);"></span> <br>
                  <span style="background-color: rgb(255, 238, 221);"> </span><a
 name="can_not_compress_encrypted_files"></a>Encrypted
files are not
compressible, containing pseudo random data - except, usually, for a
few
bytes in the file header. Plainly, there is
not a shorter, more efficient way to represent the content of the file
no matter how hard the compressor tries.<br>
                  <br>
                  <h3><span style="font-weight: bold;">Examples of non
compressible files types<br>
                  </span></h3>
Encryption can be employed to protect many types of databases, backup
files, some documents formats as PDF, and it is a common option to
protect archives. Archive formats supporting strong encryption
standards are 7Z, PEA,
RAR,
ZIP, and ZIPX.<br>
                  <br>
                  <h4><span style="font-weight: bold;">Possible
solutions
to reduce space occupation of non compressible files</span></h4>
It is not possible to compress a single encrypted file, and switching
to more powerful compression algorithms / settings is of no use, but -
as well as for previous cases - it
is possible to <span style="font-weight: bold;">de-duplicate content</span>
of archive / backup removing
unnecessary duplicate copies of the same data, reducing final size by
consequence.<br>
If even this strategy is not viable, it is possible to <span
 style="font-weight: bold;">span (split) the output</span> in multiple
volumes of desired size, smaller than
limitations in trasmission (email attachment, sharing, max upload size)
or
in storing the data (filesystem of archive format size limitations).<br>
An alternative approach is to decrypt the archive / backup image /
database before re-compressing it with a more powerful algorithm or
higher compression settings, and then re-applying encryption if
security is a concern.<br>
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                  <td
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 style="vertical-align: top; background-color: rgb(240, 239, 238);"><small><a
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OF
VIRTUAL
MACHINE DISKS</a><br>
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                  <td
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OF GRAPHIC FILES</a><br>
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EFFICIENCY</a><a href="7zip-files-utility.html"><br>
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            <p><a href="peazip-help-faq.html">FAQ</a>
&gt; Archiving &gt; Why some files types does not compress efficiently<br>
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            <p> </p>
Topics and search hints about why some file formats can not be
compressed efficiently, how to properly reduce
size of files with poor compression ratio (zip, docx, pdf, jpeg, mp3,
avi, mpeg), strategies and solutions for poorly
compressible data, encrypted, and multimedia file types
            <table style="width: 100%; text-align: left;" border="0"
 cellpadding="6" cellspacing="0">
              <tbody>
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                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">why I
cannot compress multimedia<br>
solutions to poor compression<br>
                  <h3>can not compress pdf files</h3>
why compression ratio is low<br>
                  <h4>poor compression ratio</h4>
why some file types does not compress well<br>
                  <h4>can not compress xlsx files</h4>
reduce size of jpeg, png, bmp files<br>
how to compress Office files<br>
can not compress mpeg files<br>
can not reduce size of pdf file<br>
can not reduce size of file with compression<br>
                  </td>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">solutions
for better compression<br>
                  <h3>can not compress jpeg files</h3>
cannot compress encrypted files<br>
efficiently compress multimedia<br>
can not reduce size of mp3 file<br>
can not reduce size of multimedia files with compression<br>
incremental backup to save space<br>
recompress existing rar zip archive<br>
non efficient compression<br>
                  <h4>can not compress rar files</h4>
difficult to reduce file size<br>
how to compress pdf files<br>
cannot save disk space<br>
                  </td>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">poor
compression ratio<br>
cannot compress database<br>
how to reduce size of mpeg files<br>
save space for backup<br>
                  <h3>can not compress mp3 files</h3>
                  <h4>file does not compress well</h4>
can not reduce size of database with compression<br>
solutions to compress files more<br>
can not reduce size pf avi files<br>
how to compress mp3 files<br>
                  <h4>can not compress docx files</h4>
why some file types does not compress efficiently<br>
                  </td>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">cannot
compress backup<br>
                  <h3>can not compress avi files</h3>
cannot reduce size of files<br>
strategies to compress better<br>
how to compress avi files<br>
efficient avi mp3 pdf compression<br>
                  <h4>can not compress mp4 files</h4>
can not reduce size of images with compression to archive<br>
reduce size of backup set<br>
poor compression result<br>
how to reduce size of pdf files<br>
can not compress files well<br>
can not compress zip files<br>
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            <td style="vertical-align: top;">Tag Cloud<br>
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